/Engine/Source/Runtime/Core/Public/Misc/MapErrors.h
{Actor} : Brush has non-coplanar polygons: This warning is caused when there is a brush in the level that has non-coplanar polygons. This is usually caused by using brush editing tools in geometry mode in extreme ways and can cause missing polygons in the level. This warning can be resolved by deleting the brush and recreating it.
static [FLazyName](API\Runtime\Core\UObject\FLazyName) NonCoPlanarPolys;